Endosteal electrode

ABSTRACT

An implantable tissue-stimulating device comprising an elongate electrode carrier member ( 11 ) having a plurality of electrodes thereon. The electrodes are preferably disposed in a linear array on the carrier member ( 11 ) and are adapted to apply a preselected tissue stimulation to the cochlea. The carrier member ( 11 ) is preformed from a resiliently flexible biocompatible silicone and extends from a distal end ( 12 ) to a stop member ( 13 ). The carrier member ( 11 ) is adapted for intracochlear but extraluminar insertion within the cochlea of an implantee. In particular, the carrier member ( 11 ) is adapted to be implanted in the crevice ( 21 ) between the spiral ligament ( 22 ) and the endosteum ( 23 ) of the lateral wall of the cochlea ( 20 ). This is a quite different location to the normal placement of the cochlear implant electrode array in the scala tympani ( 24 ) of the cochlea ( 20 ). The placement of the carrier member ( 11 ) is designed to avoid any breach of the internal ducts of the cochlea ( 20 ), such as the scala tympani ( 24 ) and scala vestibuli ( 25 ) so that the normal hydrodynamic behaviour of the cochlea ( 20 ) is not affected by any intrusive device. By preservng the normal hydrodynamic behaviour of the cochlea ( 20 ), use of the carrier member ( 11 ) maximises the possibility of also preserving any hearing of the implantee that is offered by the cochlea ( 20 ). Use of the device in a system for masking or treating the symptoms of tinnitus is also described.

FIELD OF THE INVENTION

The present invention relates to an auditory prosthesis adapted forintracochlear but extraluminar placement within the cochlea. Anapplication of the device for masking or treating tinnitus is alsodescribed.

BACKGROUND OF THE INVENTION

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and sensorineural. In some cases, a person mayhave hearing loss of both types. Of them, conductive hearing loss occurswhere the normal mechanical pathways for sound to reach the hair cellsin the cochlea are impeded, for example, by damage to the ossicdes.Conductive hearing loss may often be helped by use of conventionalhearing aids, which amplify sound so that acoustic information doesreach the cochlea and the hair cells.

In many people who are profoundly deaf, however, the reason for theirdeafness is sensorineural hearing loss. This type of hearing loss is dueto the absence of, or destruction of, the hair cells in the cochleawhich transduce acoustic signals into nerve impulses. These people arethus unable to derive suitable benefit from conventional hearing aidsystems, no matter how loud the acoustic stimulus is made, because thereis damage to or absence of the mechanism for nerve impulses to begenerated from sound in the normal manner.

It is for this purpose that cochlear implant systems have beendeveloped. Such systems bypass the hair cells in the cochlea anddirectly deliver electrical stimulation to the auditory nerve fibres,thereby allowing the brain to perceive a hearing sensation resemblingthe natural hearing sensation normally delivered to the auditory nerve.U.S. Pat. No. 4,532,930, the contents of which are incorporated hereinby reference, provides a description of one type of traditional cochlearimplant system.

Typically, cochlear implant systems have consisted of essentially twocomponents, an external component commonly referred to as a processorunit and an internal implanted component commonly referred to as areceiver/stimulator unit. Traditionally, both of these components havecooperated together to provide the sound sensation to a user.

The external component has traditionally consisted of a microphone fordetecting sounds, such as speech and environmental sounds, a speechprocessor that converts speech into a coded signal, a power source suchas a battery, and an external transmitter coil.

The coded signal output by the sound processor is transmittedtranscutaneously to the implanted receiver/stimulator unit situatedwithin a recess of the temporal bone of the user. This transcutaneoustransmission occurs via the external transmitter coil which ispositioned to communicate with an implanted receiver coil provided withthe stimulator/receiver unit. This communication serves two essentialpurposes, firstly to transcutaneously transmit the coded sound signaland secondly to provide power to the implanted receiver/stimulator unitConventionally, this link has been in the form of a radio frequency (RF)link, but other such links have been proposed and implemented withvarying degrees of success.

The implanted receiver/stimulator unit traditionally includes a receivercoil that receives the coded signal and power from the externalprocessor component, and a stimulator that processes the coded signaland outputs a stimulation signal to an intracochlea electrode assemblywhich applies the electrical stimulation directly to the auditory nerveproducing a hearing sensation corresponding to the original detectedsound.

Traditionally, at least the speech processor of the external componentryhas been carried on the body of the user, such as in a pocket of theuser's clothing, a belt pouch or in a harness, while the microphone hasbeen mounted on a clip mounted behind the ear or on the lapel of theuser.

More recently, due in the main to improvements in technology, thephysical dimensions of the sound processor have been able to be reducedallowing for the external componentry to be housed in a small unitcapable of being worn behind the ear of the user. This unit allows themicrophone, power unit and the sound processor to be housed in a singleunit capable of being discretely worn behind the ear, with the externaltransmitter coil still positioned on the side of the user's head toallow for the transmission of the coded sound signal from the soundprocessor and power to the implanted stimulator unit.

It is further envisaged that with continual improvements in technologyall the traditional external componentry may be implanted in the user.In such a system all of the speech processing may be performed insidethe implanted stimulator unit, via an implanted microphone.

It is known in the art that the cochlea is tonotopically mapped. Inother words, the cochlea can be partitioned into regions, with eachregion being responsive to signals in a particular frequency range. Thisproperty of the cochlea has been exploited by providing the electrodeassembly with an array of electrodes, each electrode being arranged andconstructed to deliver a stimulating signal within a preselectedfrequency range, to the appropriate region within the scala tympani ofthe cochlea. The electrical currents and electric fields from eachelectrode stimulate the nerves disposed on the modiolus of the cochlea.

Despite the enormous benefits offered by cochlear implants, onepotential disadvantage of placement of the electrode assembly within thescala tympani is that it is necessary to breach the internal ducts ofthe cochlea, generally the scala tympani. The breaching of the scalatympani of the cochlea adversely affects the hydrodynamic behaviour ofthe cochlea and is thought to prevent or at least reduce any chance ofpreservation of any residual hearing of the implantee. This can beproblematic for those persons who would benefit from use of a cochlearimplant to improve hearing of relatively high frequencies but who havesome residual hearing of relatively low frequencies. In such a case, theimplantee is forced to trade off an existing residual capacity to hearrelatively low frequency sounds against the desirability of being ableto have a hearing sensation of relatively high frequency sounds offeredby a cochlear implant.

There have been a number of proposals put forward to provide a hybridsystem whereby a cochlear implant system can be used in conjunction withresidual hearing, usually assisted by the use of a hearing aid. One suchexample of a proposed system is described in International PatentApplication No WO 00/69512. In this application, the hybrid systemutilises a hearing aid to amplify the low frequency sound enabling theuser to rely on normal hearing processes to experience such sounds. Forhigh frequency sounds, the hybrid system utilises a relativelyconventional cochlear stimulation device consisting of a short cochlearelectrode array. The short cochlear electrode array of this applicationis described as consisting of 4-8 electrodes and is inserted directlythrough the round window membrane making contact with the basal regionof the cochlea. Therefore the system as described in this applicationstill uses a relatively obtrusive electrode array making it verydifficult to preserve any residual hearing the patient may have in suchareas.

As already described, the present application is also directed to adevice for masking or treating tinnitus. Tinnitus is the medical termfor a condition in which sufferers report a ringing in their ears orhead when there is in fact no external sound present in the sufferer'saudible range. Although some people hear a ringing noise, others reportthe noise as being a hissing, a chirping, or a clicking. There arevarious estimates as to how many sufferers of tinnitus there areworldwide. For example, it is suggested that some 50 million Americanssuffer from tinnitus, with about 83% of them hearing a constant ringing.Other figures suggest at least 12 million people have tinnitus to whatis regarded as a distressing degree.

For some people, tinnitus is just a nuisance. For others, it can be aquite debilitating condition. Usually, the only relief tinnitussufferers will experience is an occasional reduction in the loudness ofthe tinnitus from time to time.

The cause of tinnitus or at least its onset is unclear. There is,however, data available that demonstrates that exposure to loud noise isa trigger for the condition. Other suggested triggers include severehead trauma, certain medications, sinus and respiratory infections, earinfections, wax build-up and certain types of tumours.

There are, as yet, no cures for tinnitus but there are severaltreatments currently used to provide at least some relief. One treatmentis the use of what are commonly referred to as tinnitus maskers. Oneexample of a tinnitus masker is disclosed in PCT Patent Application WO90/07251. Tinnitus maskers are essentially small battery operateddevices which are worn like a hearing aid behind or in the ear, andcover (mask) the tinnitus psychoacoustically by artificial sounds whichare emitted, for example, via a hearing aid speaker into the auditorycanal and which reduce the disturbing tinnitus as far as possible belowthe threshold of perception. The artificial sounds are often narrowbandnoise (for example, third octave noise) which in its spectral positionand its loudness level can be adjusted via a programming device toenable the maximum position adaptation to the individual tinnitussituation. This form of treatment is available in several forms and whenproperly administered, has been demonstrated to assist in somewherebetween 58% and 65% of cases. Masking is simply the addition of anoutside sound that serves as a substitute or mask for the tinnitus.

Masking systems known to date are typically worn within the ear canal orpositioned nearby so as to ensure provision of a masking sound to thesufferer and as a result these devices stigmatise the wearer and areworn reluctantly.

Implantable tinnitus maskers are known, such as that described in U.S.Pat. No. 5,795,287. Such devices utilise electromechanical transducerscoupled to the ossicular chain to produce the artificial masking sounds,however, these devices require a very complicated surgery to implant asthe electromechanical transducer must mechanically manipulate theossicular chain. Also, it has been found that such mechanical couplingis not always guaranteed to be stable as pressure necroses in the areaof the middle ear ossicle has been found to occur in a number of casesresulting in bone erosion.

The present invention relates to a new system for treating the symptomsof tinnitus that preferably does not require complicated surgery nor thefixation of electromechanical transducers to the ossicles.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

SUMMARY OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

The present invention is firstly directed to an implant that can beinserted in the cochlea but in a position external to the scala tympani.Such an implant provides an alternative option for those personsdescribed above who would benefit from the use of a cochlear implant toimprove hearing of relatively high frequencies but who have someresidual hearing of relatively low frequencies. The present inventionfurther preferably aims to provide a cochlear implant system thatpreserves the normal hydrodynamic nature of the cochlea allowing for anelectrode array to be positioned to stimulate the desired neuronswithout causing damage to the important internal ducts of the cochlea.

The present invention is secondly directed to an implant, as describedabove, that can be used as a means of masking the symptoms of tinnitus.

According to a first aspect, the present application is directed to afirst invention comprising an implantable tissue-stimulating devicehaving a carrier member having at least one electrode thereon, thecarrier member being adapted for intracochlear but extraluminarinsertion within the cochlea of an implantee.

According to a second aspect, the present invention is directed to asecond invention comprising an implantable tissue-stimulating device foruse in the masking or treatment of the symptoms of tinnitus, the devicehaving a carrier member having at least one electrode thereon, thecarrier member being adapted for intracochlear but extraluminarinsertion within the cochlea of an implantee.

According to a third aspect, the present invention is directed to athird invention comprising an implantable tissue-stimulating device whenused in the masking or treatment of the symptoms of tinnitus, the devicehaving a carrier member having at least one electrode thereon, thecarrier member being adapted for intracochlear but extraluminarinsertion within the cochlea of an implantee.

In the above aspects, the device can be a cochlear implant In oneembodiment, the carrier member can be a cochlear implant carrier member.The carrier member preferably has a body having a plurality ofelectrodes mounted thereon. The electrodes can be disposed in an arrayon the carrier member. The electrodes can be adapted to apply apreselected tissue stimulation.

In a preferred embodiment, the carrier member is adapted to be implantedin a crevice between the spiral ligament and the endosteum of thelateral wall of the cochlea. This is quite different to the normalplacement of the electrode array of a traditional cochlear implant inthe scala tympani of the cochlea.

The placement of the device is preferably designed to avoid any breachof the internal ducts of the cochlea (eg. scala tympani and scalavestibule) so that the normal hydrodynamic behaviour of the cochlea isnot affected by any intrusive device. This is important, as forimplantees suffering tinnitus, use of the device does not lead to lossof what otherwise may be good hearing. For implantees with at least somesensorineural hearing loss, use of the device maximises the possibilityof also preserving residual hearing offered by the implantee's cochlea.In this case, it is envisaged that use of the device will haveparticular benefit in those instances where the implantee hassubstantial residual hearing in the low frequencies but would benefitfrom supplemental stimulation in a relatively higher frequency range. Inthis case, the implantee may benefit from use of a hearing aid thatamplifies the relatively low frequencies still detectable by theimplantee and a cochlear implant for detection of relatively highfrequencies.

In a preferred embodiment, the carrier member has a maximum length ofabout 7-10 mm, a width of about 0.6 mm and a thickness no greater thanabout 0.2 mm and, more preferably, about 0.1 mm. In a furtherembodiment, the carrier member can have an inner surface and an outersurface, the inner surface being adapted to face inwardly into thecochlea, while the outer surface faces toward the endosteum of thecochlea. In one embodiment, the inner face can have a concavity. In afurther embodiment, the outer face can have a convexity.

In a further embodiment, the thickness of the carrier member between itsinner surface and outer surface can be substantially constant for atleast a majority of its length from the proximal end to the distal end.In another embodiment, the thickness of the carrier can change, such asdecrease, from the proximal end to the distal end. In a preferredembodiment, the carrier can be relatively more resiliently flexible in alongitudinal plane and relatively less resiliently flexible in a lateralplane.

The carrier member can be relatively flexible and preferably adapted tofollow the curvature of the endosteum along the basal turn. In apreferred embodiment, a proximal end of the carrier member can beidentified by a stop member. The stop member can extend substantially atright angles to the longitudinal axis of the carrier member. The stopmember preferably has a length of between about 1.5 and 2.0 mm.

The stop member can serve as both a region for grasping the carriermember and also act to prevent insertion of the carrier member withinthe crevice beyond a predetermined maximum depth.

In a still further embodiment, said at least one electrode has a surfacethat is at least adjacent the inner surface of the carrier. Morepreferably, each of the electrodes in the array has a surface that isadjacent the inner surface of the carrier member. In a furtherembodiment, the surfaces of the electrodes are aligned with the innersurface of the carrier member. In another embodiment, the surfaces ofthe electrodes stand proud of the inner surface of the carrier member.It is also envisaged that the electrode surface could also be recessedinto the inner surface of the carrier member.

In one embodiment, the carrier member can be formed from a biocompatibleelastomeric material. In one embodiment, the elastomeric material can bea silicone rubber. In another embodiment, the carrier member can beformed from a biocompatible polyurethane or similar material.

The surfaces of the carrier member are preferably smooth to prevent anydamage to the cochlea as the array is placed in the cochlea.

In a preferred embodiment, the electrode array can include electricallyconducting wires connected to the electrodes and extending to at leastsaid proximal end. In one embodiment, one wire can be connected to eachof said electrodes. In another embodiment, at least two wires can beconnected to each of said electrodes.

Each electrode can comprise a contact element. The carrier member canhave a longitudinal axis with each contact element arranged orthogonallyto the longitudinal axis. The contact elements can be formed from abiocompatible material. The biocompatible material of the contactelement can be platinum. The wires may preferably be connected to thecontact elements by welding, or any other suitable connecting method.

Once implanted, the electrodes of the carrier member preferably receivestimulation signals from a stimulator means. The stimulator means ispreferably electrically connected to the carrier member by way of anelectrical lead. The lead can include the one or more wires extendingfrom each electrode of the array mounted on the carrier member.

In one embodiment, the lead can extend from the carrier member to thestimulator means or at least the housing thereof. In one embodiment, thelead is continuous with no electrical connectors, at least external thehousing of the. stimulator means, required to connect the wiresextending from the electrodes to the stimulator means. One advantage ofthis arrangement is that there is no requirement for the surgeonimplanting the device to make the necessary electrical connectionbetween the wires extending from the electrodes and the stimulatormeans.

The stimulator means is preferably positioned within a housing that isimplantable within the implantee. The housing for the stimulator meansis preferably implantable within a recess in the bone behind the earposterior to the mastoid.

When implanted, the housing preferably contains, in addition to thestimulator means, a receiver means. The receiver means is preferablyadapted to receive signals from a controller means. The controller meansis, in use, preferably mounted external to the body of the implanteesuch that the signals are transmitted transcutaneously through the skinof the implantee.

Signals can preferably travel from the controller means to the receivermeans and vice versa. The receiver means can include a receiver coiladapted to receive radio frequency (RF) signals from a correspondingtransmitter coil worn externally of the body. The radio frequencysignals can comprise frequency modulated (FM) signals. While describedas a receiver coil, the receiver coil can preferably transmit signals tothe transmitter coil which receives the signals.

The transmitter coil is preferably held in position adjacent theimplanted location of the receiver coil by way of respective attractivemagnets mounted centrally in, or at some other position relative to, thecoils.

The external controller can comprise a processor adapted to output oneor more stimulation regimes to the stimulator.

Where the device is being used to mask or treat the symptoms oftinnitus, the external controller can comprise a processor adapted tooutput one or more stimulation regimes to the stimulator.

In one embodiment of this application, the stimulation regime cancomprise a random continuous sub-threshold stimulation regime. In thisregime, the stimulation signals output to the electrodes of the carriermember are at a level below the threshold of hearing of the sufferer.

In another embodiment, the stimulation regime can comprise a randomcontinuous supra-threshold stimulation, such as white noise.

In a still further embodiment, the stimulation regime can comprise arandom discontinuous supra-threshold stimulation regime. It ispostulated by the present inventors that irregular stimulation may besufficient to reduce the impact of the tinnitus condition. Irregularstimulation also has the advantage of being relatively power-efficientand hence would result in longer battery life for the device.

In yet a further embodiment, the stimulation regime can comprise atreatment-on-demand regime. Such a regime is postulated by the presentinventors as being advantageous for those persons who only sufferirregular episodes of tinnitus. In this embodiment, the externalcontroller can further comprise an activation means. The activationmeans can comprise a switch means on the external controller. In thiscase, the sufferer or a third person could activate the processor whenrequired.

Where the device is being used to provide a hearing sensation, theexternal controller preferably comprises a speech processor adapted toreceive signals output by a microphone. During use, the microphone ispreferably worn on the pinna of the implanted, however, other suitablelocations can be envisaged, such as the lapel of the implantee'sclothing. The speech processor encodes the sound detected by themicrophone into a sequence of electrical stimuli following givenalgorithms, such as algorithms already developed for cochlear implantsystems. The encoded sequence is transferred to the implantedreceiver/stimulator means using the transmitter and receiver coils. Theimplanted receiver/stimulator means demodulates the modulated FM signaland allocates the electrical pulses to the appropriate attachedelectrode by an algorithm which is consistent with the chosen speechcoding strategy.

In one embodiment, the processor can be adapted to receive signals fromthe microphone when external sounds, such as speech, are present and tooutput a stimulation regime, when no external sounds are present, thatis adapted to mask or treat the symptoms of tinnitus.

The external controller preferably further comprises a power supply. Thepower supply can comprise one or more rechargeable batteries. Thetransmitter and receiver coils are used to provide power viatranscutaneous induction to the implanted receiver/stimulator means andthe electrode array.

While the implant system can rely on external componentry, in anotherembodiment, the controller means, including the microphone wherepresent, the processor, and the power supply can also be implantable. Inthis embodiment, the controller means can be contained within ahermetically sealed housing or the housing used for the stimulatormeans.

An implantable controller means also preferably has an activation meansthat provides the implantee or a third person with a means to activate astimulation regime when required. In one embodiment, the inactivationmeans can comprise a magnetic switch. In this case, the implantablecontroller means would preferably incorporate a magnetic field detectorwhich is triggered on detecting the presence of a suitable magnet helddose to the location of the implantable controller.

In another embodiment, the activation means can comprise a radiofrequency switch means. In this case, the implantable controller caninclude a radio frequency detector means adapted to receive a particularpredetermined or programmed signal from a radio transmitter. The radiotransmitter is activated when required by the implantee or a thirdperson.

In yet another embodiment, the activation means can comprise an infraredswitch means. In this case, the implantable controller can include ainfrared detector means adapted to receive a particular pre-determinedor programmed infrared signal from a infrared transmitter. The infraredtransmitter is activated when required by the implantee or a thirdperson. According to a fourth aspect, the present invention is directedto a fourth invention comprising a method of inserting atissue-stimulating device as defined above into a cochlea of animplantee, the method comprising the steps of:

-   -   performing a fenestration to access the crevice of the cochlea        between the spiral ligament and the endosteum of the lateral        wall of the cochlea;    -   placing the device in the crevice; and    -   closing the fenestration.

According to a fifth aspect, the present invention is directed to afifth invention comprising a method of treating the symptoms of tinnituscomprising inserting a device as defined above into a cochlea of animplantee, the method comprising the steps of:

-   -   performing a fenestration to access the crevice of the cochlea        between the spiral ligament and the endosteum of the lateral        wall of the cochlea;    -   placing the device in the crevice; and    -   closing the fenestration.

In a preferred embodiment of the fourth and fifth aspects, the device isguided very gently through the fenestration and into the crevice.

Following placement of the device, the method can include the step ofcovering the fenestration with soft body tissue and/or bony dust mixedwith fibrin.

Once in place, the device can be used to output-one or more stimulationregimes to the cochlea to provide a hearing sensation and/or mask ortreat the symptoms of tinnitus as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, a preferred mode of carrying out the inventionis described with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of a carrier member of animplantable electrode array according to the present invention;:

FIG. 2 is a cross-sectional view through a human cochlea depicting thedesired position for placement of the electrode array according to thepresent invention; and

FIG. 3 is a pictorial representation of one embodiment of a system thatcan utilise the carrier member of FIG. 1 whether it be for providing ahearing sensation to an implantee and/or to mask or treat the symptomsof tinnitus.

PREFERRED MODE OF CARRYING OUT THE INVENTION

One embodiment of an electrode assembly for use in the present inventionaccording to the present invention is depicted generally as 10 in thedrawings.

The assembly 10 includes an elongate electrode carrier member 11. Forthe purposes of clarity, the plurality of electrodes that are mounted onthe carrier member 11 are not depicted in the drawings. While notdepicted, the electrodes can be disposed in a linear array on thecarrier member 11 and be adapted to apply a preselected tissuestimulation to the cochlea.

The depicted carrier member 11 is preformed from a resiliently flexiblebiocompatible silicone and extends from a distal end 12 to a stop member13.

The carrier member 11 is adapted for intracochlear but extraluminarinsertion within the cochlea of an implantee.

In use, the carrier member 11 is adapted to be implanted in the crevice21 (see FIG. 2) between the spiral ligament 22 and the endosteum 23 ofthe lateral wall of the cochlea 20. This is a quite different locationto the normal placement of the cochlear implant electrode array in thescala tympani 24 of the cochlea 20.

The placement of the carrier member 11 is designed to avoid any breachof the internal ducts of the cochlea 20 (eg. scala tympani 24 and scalavestibuli 25) so that the normal hydrodynamic behaviour of the cochlea20 is not affected by any intrusive device. By preserving the normalhydrodynamic behaviour of the cochlea 20, use of the carrier member 11maximises the possibility of also preserving any hearing of theimplantee that is offered by the cochlea 20.

In the depicted embodiment, the carrier member 11 has a maximum lengthof about 8-10 mm, a width of about 0.6 mm and a thickness no greaterthan about 0.1 mm. The thickness of the carrier member between its innersurface and outer surface is substantially constant for at least amajority of its length from the distal end 12 to the stop member 13,except in the region adjacent the end 12 where the thickness graduallytapers towards end 12.

The depicted carrier 11 is more resiliently flexible in a longitudinalplane and relatively less resiliently flexible in a lateral plane. Thecarrier member 11 is adapted to follow the curvature of the endosteumalong the basal turn of the cochlea 20.

As depicted, the stop member 13 extends substantially at right angles tothe longitudinal axis of the carrier member 11. The depicted stop member13 has a length of between about 1.5 and 2.0 mm.

The stop member 13 serves as both a region for grasping the carriermember 11 and also acts to prevent insertion of the carrier member 11within the crevice 21 beyond a predetermined maximum depth (eg. 8-10mm).

While not depicted, the electrode assembly 10 includes electricallyconducting wires connected to the electrodes and extending at leastbeyond the stop member 13. In the depicted embodiment, one wire can beconnected to each of said electrodes.

In use, a surgeon would perform a fenestration to access the crevice 21between the spiral ligament 22 and the endosteum 23 of the lateral wallof the cochlea 20. The carrier member 11 would then be inserted into thecrevice 21 using an insertion tool that grips the stop member 13 andguides the carrier member 11 very gently into the crevice 21. Oncepositioned, the surgeon could close the fenestration by covering it withsoft body tissue and/or bony dust mixed with fibrin.

Once implanted, the electrodes of the carrier member 11 receivestimulation signals from an implantable stimulator 30.

The stimulator 30 is positioned within a housing 31 that is implantablewithin the implantee. The housing 31 for the stimulator 30 isimplantable within a recess in the bone behind the ear posterior to themastoid.

When implanted, the housing 31 contains, in addition to the stimulator30, a receiver. The receiver is adapted to receive signals from acontroller 32. The controller 32 is, in use, typically mounted externalto the body 33 of the implantee such that the signals are transmittedtranscutaneously through the skin of the implantee. The controller 32can be worn on the body of the user or can be adapted to be worn behindthe ear of the user in much the same way as conventional hearing aiddevices.

The signals travel from the controller 32 to the receiver and vice versaby use of a receiver coil 34 adapted to receive radio frequency (RF)signals from a corresponding transmitter coil 35 worn externally of thebody 33. The radio frequency signals can comprise frequency modulated(FM) signals. While described as a receiver coil, the receiver coil 34can also transmit signals to the transmitter coil 35 which receives thesignals.

The transmitter coil 35 is held in position adjacent the implantedlocation of the receiver coil 34 by way of respective attractive magnetsmounted centrally in, or at some other position relative to, the coils.

The external controller 32 comprises a processor adapted to output oneor more stimulation regimes to the stimulator 31. It is also envisagedthat the stimulator 31 may have the capability to store one or morestimulation regimes and upon request deliver the regime to the user viathe electrodes.

In one use of the system, the stimulation regimes of the stimulator 31are designed to mask or treat the symptoms of tinnitus. In oneembodiment, the stimulation regime can comprise a random continuoussub-threshold stimulation regime. In this regime, the stimulationsignals output to the electrodes of the carrier member 11 are at levelbelow the threshold of hearing of the sufferer.

In another embodiment, the stimulation regime can comprise a randomcontinuous supra-threshold stimulation, such as white noise.

In a still further embodiment, the stimulation regime can comprise arandom discontinuous supra-threshold stimulation regime.

In yet a further embodiment, the stimulation regime can comprise atreatment-on-demand regime. In this embodiment, the external controller32 can further comprise an activation means 36. The depicted activationmeans 36 comprises a switch on the external controller 32. In this case,the sufferer or a third person could activate the processor whenrequired.

In addition to the above, the processor can be adapted to receivesignals output by a microphone (not depicted). In this case and duringuse, the microphone can be worn on the pinna of the implantee, however,other-suitable locations can be envisaged, such as a lapel of theimplantee's clothing. In this case, the processor can encode the sounddetected by the microphone into a sequence of electrical stimulifollowing given algorithms, such as algorithms already developed forcochlear implant systems. The encoded sequence is then transferred tothe implanted stimulator 30 using the transmitter and receiver coils.The implanted stimulator 30 demodulates the FM signals and allocates theelectrical pulses to the appropriate attached electrode by an algorithmwhich is consistent with the chosen speech coding strategy.

The housing of the external controller 32 further houses a power supply.In the depicted embodiment, the power supply comprise one or morerechargeable batteries. The transmitter and receiver coils are used toprovide power via transcutaneous induction to the implanted stimulator30 and the electrode array 10.

While the implant system can rely on external componentry, in anotherembodiment, the controller, including the microphone where present, theprocessor, and the power supply can also be implantable. In thisembodiment, which is not depicted, the controller can be containedwithin a hermetically sealed housing or the housing used for thestimulator.

An implantable controller means would typically have an activation meansthat provides the implantee or a third person with a means to activate astimulation regime when required. In one embodiment, the inactivationmeans can comprise a magnetic switch. In this case, the implantablecontroller would preferably incorporate a magnetic field detector whichis triggered on detecting the presence of a suitable magnet held closeto the location of the implantable controller.

In another embodiment, the activation means can comprise a radiofrequency switch means. In this case, the implantable controller caninclude a radio frequency detector means adapted to receive a particularpredetermined or programmed signal from a radio transmitter. The radiotransmitter is activated when required by the implantee or a thirdperson.

In yet another embodiment, the activation means can comprise an infraredswitch means. In this case, the implantable controller can include ainfrared detector means adapted to receive a particular predetermined orprogrammed infrared signal from a infrared transmitter. The infraredtransmitter is activated when required by the implantee or a thirdperson.

The present invention provides an implantable device that can be used toprovide a hearing sensation to an implantee with sensorineural hearingloss and or mask or treat the symptoms of tinnitus while preserving thehearing of the implantee's cochlea into which the stimulating electrodearray has been inserted.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. An implantable tissue-stimulating device having a carrier memberhaving at least one electrode thereon, the carrier member being adaptedfor intracochlear but extraluminar insertion within the cochlea of animplantee.
 2. An implantable tissue-stimulating device for use in themasking or treatment of the symptoms of tinnitus, the device having acarrier member having at least one electrode thereon, the carrier memberbeing adapted for intracochlear but extraluminar insertion within thecochlea of an implantee.
 3. An implantable tissue-stimulating devicewhen used in the masking or treatment of the symptoms of tinnitus, thedevice having a carrier member having at least one electrode thereon,the device being adapted for intracochlear but extraluminar insertionwithin the cochlea of an implantee.
 4. An implantable tissue-stimulatingdevice of claim 1 wherein the carrier member has a body having aplurality of electrodes mounted thereon.
 5. An implantabletissue-stimulating device of claim 4 wherein the electrodes are disposedin an array on the carrier member and are adapted to apply a preselectedtissue stimulation.
 6. An implantable tissue-stimulating device of claim1 wherein the carrier member is implantable in a crevice between thespiral ligament and the endosteum of the lateral wall of the cochlea. 7.An implantable tissue-stimulating device of claim 6 wherein the carriermember has a maximum length of about 7 mm-10 mm, a width of about 0.6 mmand a thickness no greater than about 0.2 mm and, more preferably, about0.1 mm.
 8. An implantable tissue-stimulating device of claim 6 whereinthe carrier member has an inner surface and an outer surface, the innersurface being adapted on implantation to face inwardly into the cochlea.9. An implantable tissue-stimulating device of claim 8 wherein the innerface has a concave surface and the outer face has a convex surface. 10.An implantable tissue-stimulating device of claim 1 wherein a stopmember extends outwardly from the carrier member substantially at rightangles to the longitudinal axis of the carrier member.
 11. Animplantable tissue-stimulating device of claim 10 wherein the stopmember has a length of between about 1.5 and 2.0 mm.
 12. An implantabletissue-stimulating device of claim 1 wherein the electrodes of thecarrier member receive stimulation signals from an implantablestimulator means.
 13. An implantable tissue-stimulating device of claim12 wherein the stimulator means is housed within a housing that alsohouses a receiver means that is adapted to receive signals from acontroller means.
 14. An implantable tissue-stimulating device of claim13 wherein the controller means comprises a processor means adapted tooutput one or more stimulation regimes to the stimulator.
 15. Animplantable tissue-stimulating device of claim 14 wherein, where thedevice is being used to mask or treat the symptoms of tinnitus, thestimulation regime is selected from the group comprising a randomcontinuous sub-threshold stimulation regime, a random continuoussupra-threshold stimulation regime, and a random discontinuoussupra-threshold stimulation regime.
 16. An implantabletissue-stimulating device of claim 14 wherein, where the device is beingused to mask or treat the symptoms of tinnitus, the stimulation regimecomprises a treatment-on-demand regime.
 17. An implantabletissue-stimulating device of claim 16 wherein the controller meansfurther has an activation means that allows the implantee or a thirdperson to activate the processor means when required.
 18. An implantabletissue-stimulating device of claim 14 wherein, where the device is beingused to provide a hearing sensation, the controller means comprises aspeech processor adapted to receive signals output by a microphone andencode the sound detected by the microphone into a sequence ofelectrical stimuli following given algorithms.
 19. An implantabletissue-stimulating device of claim 18 wherein the speech processor isadapted to receive signals from the microphone when external sounds,such as speech, are present and to output a stimulation regime, when noexternal sounds are present, that is adapted to mask or treat thesymptoms of tinnitus.
 20. An implantable tissue-stimulating device ofclaim 14 wherein the controller means is implantable and containedwithin a hermetically sealed housing or a housing used for thestimulator means.
 21. An implantable tissue-stimulating device of claim20 wherein the controller means has an activation means that providesthe implantee or a third person with a means to activate a stimulationregime when required.
 22. A method of inserting a tissue-stimulatingdevice as defined in claim 1 into a cochlea of an implantee, the methodcomprising the steps of: performing a fenestration to access the creviceof the cochlea between the spiral ligament and the endosteum of thelateral wall of the cochlea; placing the device in the crevice; andsealing the fenestration.
 23. A method of treating the symptoms oftinnitus comprising inserting a device as defined in claim 1 into acochlea of an implantee, the method comprising the steps of: performinga fenestration to access the crevice of the cochlea between the spiralligament and the endosteum of the lateral wall of the cochlea; placingthe device in the crevice; and sealing the fenestration.